In an internal combustion engine (hereinafter, simply referred to as an “engine”) of a vehicle or the like, a combustible gas mixture is prepared by mixing fuel injected from a fuel injection unit and the air introduced through an intake pipe and is combusted inside a cylinder. In such an engine, it is known that a mixing state between the air and the fuel injected from the fuel injection unit significantly affects engine performance. In particular, atomization of the fuel injected from the fuel injection unit is an important factor for engine performance.
In this fuel injection unit, a nozzle plate is installed in a fuel injection nozzle of a valve body in order to promote atomization of the sprayed fuel, so that the fuel is injected from a plurality of small nozzle orifices provided on this nozzle plate.
FIGS. 15A and 15B illustrate a nozzle plate 100 of the background art. The nozzle plate 100 of FIGS. 15A and 15B has a stack structure obtained by stacking the first and second nozzle plates 101 and 102. As illustrated in FIGS. 15A, 15B, 16A, and 16B, the first nozzle plate 101 is provided with a pair of first nozzle orifices 103A and 103B that penetrate through front and rear surfaces and are arranged in axial symmetrical positions with respect to a center line 105 extending along the X-axis on the center line 104 extending along the Y-axis. In addition, as illustrated in FIGS. 15A, 15B, 17A, and 17B, the second nozzle plate 102 is provided with a pair of second nozzle orifices 106A and 106B arranged in axial symmetrical positions with respect to the center line 104 extending along the Y-axis on the center line 105 extending along the X-axis direction. A pair of second nozzle orifices 106A and 106B communicate with the first nozzle orifices 103A and 103B through a pair of curved grooves 108A and 108B (first and second curved grooves 108A and 108B) formed in a face (surface) 107 side of the first nozzle plate 101 where the fuel impinges. In addition, the second nozzle plate 102 communicates with a pair of curved grooves 108A and 108B through a communication groove 110 extending along the center line 104.
In the nozzle plate 100 of the background art illustrated in FIGS. 15A and 15B, the fuel injected from the fuel injection nozzle of the valve body is introduced into the curved grooves 108A and 108B from the first nozzle orifices 103A and 103B, and the fuel flowing into the curved grooves 108A and 108B flows out from the second nozzle orifices 106A and 106B while making a rotary motion by virtue of the curved grooves 108A and 108B. As a result, improvement of fuel atomization quality is promoted (see Japanese Unexamined Patent Publication No. H10-507240).
However, as illustrated in FIGS. 15A and 15B, in the nozzle plate 100 of the background art, the first and second curved grooves 108A and 108B used to allow the first nozzle orifices 103A and 103B and the second nozzle orifices 106A (106B) to communicate with each other have different lengths. Therefore, a flow rate of the fuel flowing from the first nozzle orifice 103A to the second nozzle orifice 106A (106B) through the first curved groove 108A becomes different from a flow rate of the fuel flowing from the first nozzle orifice 103B to the second nozzle orifice 106A (106B) through the second curved groove 108B. This disadvantageously causes a variation in the spray (a variation in fuel particle size and a variation in concentration of the fuel particle in the spray) generated by injecting fuel from the second nozzle orifice 106A (106B).
In view of the aforementioned problems, it is therefore an object of the present invention to provide a nozzle plate capable of uniformly spraying fuel.